10 Water Level Control
Mk8 MM Manual Page | 157
10 WATER LEVEL CONTROL
10.1 Overview
10.1.1 Safety
The purpose of a steam boiler is to generate steam in a safe and efficient manner. The heat produced from
the fuel combustion is transferred to the water in the boiler. The water evaporates to steam under pressure.
The boiler manufacturer will have designed the boiler so that the steam is drawn out from the header at a
safe rate.
As the steam is released, water must be fed into the boiler at the same time to ensure that the water level
does not reach a critical low. If the burner continues to fire with no enough water in the steam boiler, serious
damage can occur and there is a high risk of an explosion due to the boiler’s metal overheating. Hence, the
water level in a steam boiler must be continuously monitored and controlled so that when firing there is
always sufficient amount of water in the boiler.
Depending on where the steam boiler is operating, there are local codes and regulations regarding the safe
operation of the steam boiler, all these codes and regulations must be adhered to.
10.1.2 Autoflame Water Level Control
Autoflame Water Level control in the Mk8 MM focuses on safety and accuracy in controlling the water level in
a steam boiler. The intelligent water level control includes high water alarms, 1
st
low and 2
nd
low alarms.
Alarm level reporting deals with the ability to determine whether the current water level in the boiler is above
or below a pre-determined level. These levels vary with each installation and must therefore be programmed
on site by a qualified commissioning engineer.
The feedwater flow is managed by 3-element control, in response to the water level measured by the level
sensing devices’ readings, boiler pressure and the burner’s firing rate. The flow is controlled by a fully
modulating feedwater/VSD or by using an on/off signal from a feedwater pump. The feedwater going into the
boiler can be controlled in the following ways by setting expansion option 2:
• Pump on/off only.
• Pump on/off and servomotor control.
• Pump on/off and VSD control.
• Pump on/off, servomotor and VSD control.
The Autoflame 3-element level control has been granted a worldwide patent; being the only system that can
combine firing rate, steam pressure and water level within one controller for the purpose of improving
feedwater control. Safety, accuracy and integrity are guaranteed.
The levels which are commissioned when using capacitance probes and/or external level sensing 4-20mA
device include high, control point, 1
st
low, 2
nd
low and end of probe.
The level of the water in the boiler should be maintained appropriate to the amount of steam being
generated. Should the water level drop below this ideal level by an excessive amount, it is necessary to stop
the burner firing. If there is insufficient water in the boiler, damage may occur to its structure, and in extreme
cases, an explosion. The water level control herein is designed to maintain a satisfactory level of water in the
boiler, whilst controlling and reporting low water level conditions.
Traditional feed water control manages water level in the boiler, steam flow and feed water flow separately,
whereas the Autoflame feed water control coordinates the water level, firing rate and steam pressure
simultaneously.
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